For high-speed digital-communication transmitter-driver design, precise output amplitude level control is often necessary, especially when utilizing finite impulse response (FIR) filter functionality. Because of the relatively large voltage-swing requirement for various standards such as IEEE 802.3ap 10GBASE-KR, and IEEE 802.3ak 10GBASE-CX4, previous methods for current mirroring between control circuits and output drivers tend to introduce large amplitude variation at the output of a transmitter.